Cryogenic refrigerators have been used since the 1960's for infrared detector cooling (for example, for military use). The compressor portion of the Stirling cryogenic cooler consists of two sets of pistons and springs that are placed 180.degree. out of phase with respect to each other. This is schematically illustrated in FIG. 2 as will be discussed later. In order to improve a mean time to failure operation, Madni U.S. Pat. No. 5,734,593 discloses a fuzzy logic controller for such a system which provides a control output signal which controls the final cooling power of the cooler-compressor of the Stirling system. Such output signal, as disclosed in the Madni '593 Patent, is a pulse width modulated (PWM) signal of the square wave type.
In driving a compressor, especially of the Stirling type, it is known that a sine wave drive, for example, accomplished by a rotating wheel and crank, is preferable for some modes of operation. However, in a cryogenic system as used in the present applications, that is an infrared detector, or in medical applications, both power requirements and size would effectively eliminate the use of such a sinusoidal drive.